0949409f1b
As part of inter-procedural optimizations (IPA), the compiler may
perform tasks such as constant propagation for functions. This involves
generating a specialized version of a given function with a new symbol
name that includes a suffix. For example, during constant propagation,
the compiler might create a specialized version named
`spiflash_start_core.constprop.0` for the `spiflash_start_core`
function. Additionally, the compiler may generate multiple clones of a
single function. Currently, when ldgen performs symbol placement, it
does not account for these compiler-generated functions, leading to
their incorrect or unexpected placement in memory (markers).
Consider a linker fragment with:
```
[mapping:spi_flash]
archive: libspi_flash.a
entries:
esp_flash_api: spiflash_start_core (noflash)
```
The `spiflash_start_core` function should be placed in IRAM. However,
the compiler might generate an optimized version of this function with a
`.constprop.0` suffix, resulting in a
`.text.spiflash_start_core.constprop.0` input section. Currently, ldgen
does not handle this situation, leading to misplaced symbols.
Since `.` is not allowed in C identifiers, it should be safe to consider
all input sections for a symbol with any `.` suffix as representing that
symbol. This means considering the symbol suffixes should not cause any
ambiguity.
This change automatically places all input sections, including those
with possible suffixes for a given symbol, into the specified memory. In
other words, specifying a function name like `spiflash_start_core` in a
linker fragment automatically includes input section names matching
`spiflash_start_core(\..*)?$`.
Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>
Linker Script Generator
Contains code that implements linker script generation, ldgen. For more information about the feature,
see docs/en/api-guides/linker-script-generation.rst.
Source Files
The following are the source files in the directory:
ldgen.py- Python executable that gets called during build.entity.py- contains classes related to entities (library, object, symbol or combination of the above) with mappable input sections.fragments.py- contains classes for parsing the different types of fragments in linker fragment files.generation.py- contains bulk of the logic used to process fragments into output commands.sdkconfig.py- used for evaluating conditionals in fragment files.linker_script.py- augments the input linker script template with output commands from generation process to produce the output linker script.output_commands.py- contains classes that represent the output commands in the output linker script.ldgen_common.py- contains miscellaneous utilities/definitions that can be used in the files mentioned above.
Tests
Unit tests are in the test directory. These tests are run as part of CI in the job test_ldgen_on_host.
There is also a test app for ldgen in tools/test_apps/build_system/ldgen_test.
Build System
Linker script generation is a part of the build process. The build scripts tools/cmake/ldgen.cmake
and make/ldgen.mk contain the build-system-side implementation for CMake and Make, respectively.
Basic Flow
The build system invokes ldgen.py, passing some information from the build.
The linker fragment files are parsed by fragments.py, evaluating conditional expressions
with sdkconfig.py.
From the parsed fragments, generation.py generates output commands defined in output_commands.py,
with some help from entity.py.
linker_script.py writes the output linker script, replacing markers with output commands generated.
More details about the implementation are in the respective source files.